The Miracle of Parallel Evolution

3 Julho, 2013

By Piotr Naskrecki - I have been going through photos taken during a recent trip to Mozambique, and every now and then I am struck by the similarity of some of the African organisms to their counterparts on other continents. One of the best such examples is that of Neotropical glass frogs (Centrolenidae) and some African reed frogs (Hyperoliidae). Their resemblance to each other is uncanny – the two animals display a virtually identical, nearly translucent body, and only the shape of their toe pads reveals which is which. And yet these two lineages of frogs are separated by at least 150 million years of evolution, with many forms that look nothing like them in between, but ended up evolving the same, homologous morphology.*) These two groups differ quite significantly in their biology, however. The South and Central American glass frogs are forest animals, spending most of their life in the trees, often high in the rainforest canopy. They lay their eggs on the underside of leaves that hang over fast flowing streams. Males of these frogs often guard multiple egg clutches, until hatching tadpoles are washed off by rain into the stream below. The African “glass frogs”, members of the Hyperolius nasutus species complex and a few others, have a very different lifestyle, and are found in open, grassy areas of the southern part of the continent. They lay eggs underwater in big clumps attached to submerged plant stems, and exhibit no parental care.

Photo: Herpetologists, can you tell which is which? Left: Centrolenella spinosa from Costa Rica, right: Hyperolius cf. pusillus from Mozambique.

Seems to me that parallel evolution is another argument against the existence of a magical intelligent designer – if the designer is intelligent enough to invent loa loa and the HIV virus, why are so many of its designs so incredibly repetitive? (I say “its” because if this omnipotence exists, I cannot imagine that it sports a set of male, or any other, genitalia.) If I could create anything I would at least give some frogs laser eyes. Or make tiny dragons with wings. Oh, wait.

Photo: One distinguishing feature of true glass frogs is the position of their eyes, which point forward, giving them more human-like appearance.

Photo: African reed frogs, like this Hyperolius cf. pusillus from Gorongosa National Park in Mozambique, have more typical eyes, positioned on the sides of the skull.

*) Parallel evolution is different from convergent evolution in that in the former similar structures evolve independently but use homologous elements e.g., pterodactyl and bat wings, whereas in the latter similar solutions are developed by using unrelated, non-homologous elements e.g., shells of ostracod crustaceans and clams.